Man, I cannot believe I did not know about this before. Cassette has some pretty decent documentation, and I have combed over it, but either this was never listed before or I just missed it. I am using v1.2, and I recently noticed there is a v2. In the upgrade notes, there is a mention that the diagnostics page moved. I had no idea there was a diagnostics page!

For example http://localhost:2452/_cassette#stylesheets (debugging locally, obviously) produces this nice little dashboard:

Cassette diagnostics dashboard

I wish I would have found this a few months ago…